The present invention relates to a method and a device for recording data from parameter values captured or ascertained in a vehicle, particularly by using sensors, especially for reconstructing accidents, and to a storage device for recording such data.
For the purpose of ascertaining the course of an accident in vehicles having an antilock braking systems (ABS) it is known from European Patent No. EP 0 078 807 B1 store travel condition quantities such as vehicle speed, braking distance and braking deceleration captured by sensors and calculable, in order to reconstruct the accident from this, since vehicles having ABS mostly do not leave behind clear skid marks.
Accident data printers are introduced in an article in Wirtschaftswoche, No. 10, page 60 to 62, of Mar. 3, 1989 (xe2x80x9cBlack Box im Autoxe2x80x9d) (Black Box in the Automobile). The accident data printer is operated by sensors which pick up all the motion changes of the automobile. Additional data (such as light or blinker switch position, steering, pedal or clutch motions, etc) can be registered. All the data are stored on a chip and overwritten every 30 seconds with up-to-date data. In case of an accident, the chip""s contents are frozen, and, until the automobile comes to a stop, further data are recorded. Finally, an accident data printer and a method of analyzing the occurrence of an accident are known from German Patent No. DE 195 09 711 A1. There, the attempt is made to minimize the great inaccuracy in determining accident data (speed and braking distance) by making use of GPS (Global Positioning System) signals for the evaluation, in addition to the data from the accident data printer. Hereby, a sufficiently exact relative position finding can be made, the absolute position finding (zero-point correction) being made by the known accident data printer. This document takes up the problem that, in order to obtain a sufficiently accurate calculation of the accident data using a customary accident data printer, an individual sensor would be required for each of the three translational and each of the three rotational degrees of freedom of the vehicle movement, which would result in an unacceptable computational and sensor-technical effort.
Actually, evidence on vehicle dynamics during an accident (mostly connected with abrupt braking, skidding or crash) requires capturing parameters at an interval such as 20-40 ms, and, for some parameters, such as wheel-speed, at less than 20 ms. On the assumption that 70 parameters are captured for accident reconstruction every 20 ms at a scope of 2 bytes over a time span of 30 ms, this would require a memory of 205 kByte.
The method described in German Patent No. DE 195 09 711 A1 for accident reconstruction, using GPS signals, requires a corresponding receiving system and likewise a substantial effort with respect to technical computations. Besides, retrofitting existing systems turns out to be difficult.
A further disadvantage of known accident printers is the long transmission time of data recorded in a volatile memory (RAM) to a non-volatile memory (e.g. EEROM). Typically, the RAM content is written into an EEPROM via a serial bus, such as the SPI. The transmission time grows linearly with the number of bytes to be transmitted. The slow transmission rate (e.g. 10 ms/byte) is unsuitable for transmitting the necessary volume of data for the actualization of an accident data memory functionality, after a crash in which there has been a probable collapse of the supply voltage as a result of damage to components of the vehicle""s electrical system, or a specific disconnecting of the battery after detection of the accident.
Accident data printers are also known in which the corresponding data are not transmitted from a RAM to an EEPROM. For example, it is possible to configure the RAM battery-buffered, this actual construction being known in at least one commercially available accident data printer. However, in control equipment, battery-buffering is regarded as very unfavorable, since these do not have their own batteries, and the vehicle electrical system can break down during an accident. As was already mentioned, however, if data are to be transmitted in control equipment from a RAM to an EEPROM, a serial bus is frequently installed.
It is an object of the present invention to provide a method and a device for recording data from parameter values captured by means of sensors in a vehicle, particularly for the reconstruction of accidents, as well as a memory device for recording such data, it being possible to record all relevant data continuously using low memory volume, and to save it in a short period of time.
In addition, the present invention relates to a computer program, on a storage medium or data carrier, which, by being run on a computer or a control device executes a method according to the present invention. In this regard, the referenced storage medium can be permanently integrated into the computer or the control device, as, for instance, a RAM, E(E)PROM, flash EPROM, hard disk, etc., or it can be mobile, such as a diskette, CD-ROM or the like.
According to the present invention, the parameter values and/or data calculated from them are recorded at increasing time intervals at decreasing density for an instantaneous capturing point in time. For it has been shown that a high recording density is required in only a very short time space before an accident, since at that time high rates of change are probable in the parameter values. Values going back farther in time can be recorded at lesser resolution, since lower rates of change can be assumed, and the relevance of the data decreases with increasing time interval from the accident.
According to the present invention, the recording density can decrease, for example, exponentially, linearly or step-wise with increasing time interval from the instantaneous capturing point in time (that is, from the possible accident point in time). It is advantageous and easily feasible in practice to record the parameter values at discretely decreasing recording frequency, a suitable, predefined number of steps (such as 2 to 8, advantageously 3 to 6) being set to cover the recording time space.
In a particular embodiment of the method according to the present invention, representative data, such as extreme values or mean values are calculated from the captured parameter values and recorded. This is advantageous particularly when the data are recorded at a very low recording frequency. Then the information which has been lost because of the large interval in the recording points in time can be partially compensated. For example, the minimum value, the maximum value and the mean value of a parameter can be calculated between two recording times and stored. In this manner important data can be maintained, and yet fewer values can be recorded than if the recording frequency were at a maximum.
The method according to the present invention cannot only be applied to the reconstruction of vehicle accidents by the use of recorded data, but also, for example, for the evaluation of parts requirements, for the determination of the service life and/or the wear of individual parts, etc., provided that the parameters needed for this are measured or otherwise ascertained by the use of suitable sensors. The time period for recording and the timing of the recording frequency has to be established for each application and each parameter. For example, the data can be evaluated along the lines of when the exchange of a replacement part is indicated, judging from the stress up to the present.
It is advantageous for accident reconstruction if the recorded data are transmitted in parallel to a nonvolatile memory after a vehicle accident. The transmission time then no longer grows linearly with data volume, but rather, immediate storage is possible after an accident or a specific event.
Furthermore, the subject matter of the present invention is a memory device for recording data from parameter values captured by sensors in a vehicle, particularly for the reconstruction of accidents, a RAM (random access memory) for recording the data, each time for a certain time period, and a nonvolatile memory being installed, to which the recorded data from the RAM can be transmitted in parallel.
An accident can be recognized in various ways. Either the vehicle electrical system collapses because of damage to its components, or the accident is detected by sensor, special detection algorithms being used for this. In that case, it is necessary to save the recorded volume of data in a nonvolatile manner in as short a period of time as possible. In other applications too, it can be desirable to permanently save the recorded data immediately after a specific event.
For this purpose, according to the present invention, a so-called nvSRAM (nonvolatile static random access memory) is used. During normal operation, the SRAM replaces the RAM, and is connected in parallel to a nonvolatile memory (such as an EEPROM). The circuit is set in such a way that, if the supply voltage falls below a specified threshold value, or at the occurrence of a specified event, the entire SRAM content is saved in less than 10 ms.
Alternatively, any other storage technology can be applied, if it permits nonvolatile storage in brief time, e.g. in a few milliseconds (ms), of larger data volumes, e.g. several kilobytes (kbytes). Examples for this are FeRAM (ferroelectric RAM) and Flash-Banks (flash memory).
The use of an ASIC (application-specific integrated circuit) in the control unit of the vehicle is particularly suitable for the implementation of an accident data storage functionality in the vehicle. Many sensors do not communicate with the vehicle bus, but are connected to the control unit (directly or via the field bus). For this purpose, the control unit makes available sensor data over the bus. Thereby structures present anyway can be optimally used. The data supplied by the sensors are further used for accident reconstruction, the sensor data being available over the vehicle bus (e.g. CAN), and the desired data are evaluated using software. An ASIC is particularly advantageous when an nvSRAM is used for data storage. Simply fitting the control unit with the ASIC is required without further hardware changes; the required software changes are minimized. Selective outfitting with the accident data memory functionality is possible.